Specific binding reactions, such as antibody-antigen reactions, have been used extensively in immunoassays to detect and/or quantify a variety of drugs or other compounds of interest in biological fluids. Such immunoassays have been developed for the determination of antigens such as proteins, as well as small molecules (haptens).
Haptens are by definition molecules too small to stimulate the production of antibodies when administered to an animal; that is, haptens by themselves are not immunogenic. However, it is well known that a hapten can be made immunogenic by conjugating it to an appropriate carrier material, which will elicit an immunogenic response when injected into a host animal.
Opiates are a class of alkaloid produced by plants of the poppy family. The most common opiates produced by the poppy plants are morphine and codeine. These opiates have been used for centuries to prevent pain but their continued use leads to addiction. Synthetic analogues of morphine also exhibit the narcotic and addictive properties of the natural opiates and include heroin, hydromorphone, hydrocodone, oxycodone and oxymorphone. These opiates (natural or synthetic) have closely related chemical structures. The illict use of opiates has resulted in a medical requirement for specific antibodies to each opiate, for use in diagnostics to rapidly detect the corresponding opiate and its metabolites in order to monitor and treat opiate addiction.
Oxycodone is a narcotic and analgesic pain-killer, and as a semi-synthetic derivative of morphine can be very addictive. The oxycodone metabolites are noroxycodone and oxymorphone.
To date, the determination of oxycodone and its metabolites in biological fluids has been based mainly on gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC). These chromatographic methods provide excellent sensitivity and selectivity but require derivatisation of oxycodone and its metabolites. These methods are, in addition, too costly and time-consuming for use as screening tools.
Radioimmmunoassays are very sensitive, but require radionuclide tracers, for example 1251I and 3H, and, in some cases, a preliminary extraction step. There are no known RIAs for oxycodone.
Enzyme-linked immunosorbent assays (ELISAs) are a non-radioactive alternative that could be used for the qualitative and quantitative determination of oxycodone and its metabolites. Again, there are no known ELISAs for oxycodone.
There is a need for oxycodone conjugates and their application to immunoassays for quantifying oxycodone and its metabolites without cross-reactivity to the opiates family in biological fluids.